The invention pertains to a shielding jacket for electrical and electronic wires and cables, and more particularly, to a novel construction of the ends of an electrical shield and an end reinforcement for the casing of the jacket.
It is common to use a shielding jacket placed over one or more conductors when either it is necessary to contain electromagnetic emissions from the conductors or to protect the conductors from external electromagnetic emissions. In accordance with Gauss' Law, it would be optimal to surround the protected conductors with a grounded conductive surface. As placing a solid metal tube around a conductor would be highly impractical, the typical shielding jacket uses some form of wire mesh electrical shield which surrounds the conductor. In a closable jacket, the shield is generally formed in an elongated, approximately rectangular shape and then wrapped around the conductor to form a tube. Some form of flexible casing similarly surrounds the shield. When such a mesh shield is used, the size and type of mesh is chosen based upon the specific ranges of frequency of the emissions which are to be shielded against. Typically, a mesh does a poor job of shielding against emissions of a wave length substantially smaller than the size of the openings in the mesh.
In a prior shielding jacket manufactured by the applicant, the rectangular shield is formed by flattening a knit wire sleeve. At the ends of the flattened sleeve the wires are cut across the ends and the two layers formed by the flattened sleeve are resistance welded together by a single pass of a rolling element resistance welder. The resistance welding serves to help prevent the mesh from fraying, which would diminish its shielding ability, as well as to prevent small pieces of wire created by the cutting from getting into and damaging either the conductors that are to be shielded or the equipment with which they are used. In the prior product a flexible polyvinyl chloride (PVC) casing in the form of a long sheet with a zipper along its edges is provided to surround the shield. A heavy braided wire conductor (braid) extends along the length of the sheet for both mechanical reinforcement and to enable a connection to a ground. The shield is disposed flat against the casing. The braid is disposed against the shield running centrally along the shield and is stitched through to the casing using a cloth thread. In operation the shield and casing are wrapped around the conductor which is to be protected. The casing is then zipped up around the shield, and the wire braid may be connected to a ground source such as a connector housing.
Despite the resistance welding of the cut end of the mesh shield, as the wire ends are still exposed, they will nevertheless have a tendency to unravel. This is so because even relatively light mechanical stimulation can break the weak bonds created by the resistance welding. It has been further observed that circumferential tension at the ends of the casing may cause the zipper to unzip and, thereby, unwrap the shield and expose the conductor.
It is therefore desirable that a flexible, closable shielding jacket be constructed so as to strengthen the mesh shield end against unraveling and to strengthen the casing end against unzipping.